The invention relates to a coating material, which contains a vehicle, which is a mixture of an ester-soluble nitrocellulose, a hydroxy-functional copolymer and a lacquer polyisocyanate, aside from pigments and/or extenders, solvents and optionally conventional lacquer auxiliaries. The coating material of the invention is particularly suitable for the production of primers as well as of extenders, especially for the motor vehicle sector, since it is possible to achieve layer thickness of up to 500 .mu.m with the coating material of the invention.
Coating materials based on polyhydroxyl polyacrylate resins and lacquer polyisocyanates are well known. For example, a coating material is described in the German Auslegeschrift No. 2,460,329, which is suitable for an automobile finishing coat and which contains a vehicle based on an acrylate resin, which has copolymerized units of 10 to 50 parts by weight of a hydroxyalkyl ester of (meth)acrylic acid. 0 to 80 parts by weight of styrene or styrene derivatives, 10 to 90 parts by weight of a (meth)acrylate ester with up to 12 carbon atoms in the alcohol group and 0 to 50 parts by weight of an .alpha.,.beta. of a monounsaturated olefinic mono- or dicarboxylic acid. Such acrylate resins, together with lacquer polyisocyanates and cellulose derivatives, are used as leveling agents. However, it has turned out that such coating materials in actual fact, as stated in the German Auslegeschrift No. 2,460,329, can only be used for finishing coats, since they are not suitable for forming thicker layers. For example, it is not possible with the known coating materials described above to dry layers, which are more than 150 .mu.m thick, with radiators, since bubbles are formed and the coatings, so obtained, are therefore not bubble-free.
A primer, primer fillers or fillers must meet various requirements. It should be appliable without problems. For example, it should level out well, even when applied on vertical surfaces or at different viscosities. Moreover, good surface drying, through-drying and sandability (dry and in the wet state) must be assured. Furthermore, the solvent resistance should be such that, when sprayed with a two-component finishing coat, a paint coat in good condition is guaranteed. In the case of filler, it should be possible to obtain a coating up to 300 .mu.m or even 500 .mu.m thick, without encountering drying problems due to the tendency to form bubbles.
Any reference herein to a "primer" coat intends to include also reference to a "filler" which refers to a coating layer in a multi-layer coating, which is applied over the primer coating, usually to promote achievement of a smooth surface which is ultimately obtained by an additional coating, such as a finish coat.